SCDi

TECHNICAL CHARACTERISTICS:

The integrated digital control system SCDi includes the following elements (elements not usually included by other suppliers in bold):

Set of internal elements:

• System to collect generator speed without external mechanical elements.
• Control of speed with control of the regulating systems with proportional valves.
• Automatic synchronization with voltage, frequency and phase equalization.
• Regulation of the intake function of the criteria of exploitation and the number of regulatory systems involved.
• Digital control of the exciter of the generator with no-load voltage setpoints and reactive energy generated.
• Control of all the elements of the power plant such as input valves, bypass, regulation pumps, greasing groups, etc.
• Protection and control of bearing temperatures, windings and cooling systems.
• Protection and control of electrical magnitudes of generation.
• Remote control system via telephone network with production history management, alarms, remote control of orders, sending of orders, etc.
• Remote control system by spoken message for four telephone numbers definable from the control program.
• Local control system by means of visualizer to see all the variables, as well as the alarms that have occurred.

Set of external elements:

• Ultrasonic level or flow sensors.
• Position sensors of regulating systems.
  

SCHEME OF THE SCDi SYSTEM:

SCHEME OF NON SCDi SYSTEM:

The SCDi regulation system offered by our company contemplates all the needed elements of the operation of the power plant as a single element in which is all the information referring to all the systems, this forces to digitalize all the exterior variables and to choose a programmable control with important benefits which causes an increase of the product cost initially, but at the same time, makes it profitable as follows:

• Elimination of multitude of scattered elements of significant cost
• Facility for the installation of monitoring systems
• Facility for installation of telecontrol systems
• Reduced commissioning time
• Reduced maintenance cost
  

USUAL CONTROL SYSTEM

The usual regulation and control systems for mini-power plants are based on dispersed controls in which independent elements execute specific functions such as: speed regulation, synchronism, excitation, voltage equalization, load distribution, production optimization, telecontrol, protection and control of auxiliary maneuvers.

These functions appear in most control applications, which we might call scattered, this requires a general supervisory element that collects the usually limited information of the different systems and acts on them, this makes adaptations difficult and sometimes prevents or makes quite expensive to carry out remote management, setpoint modification or switching systems, since each element is constructed with an objective point of view that may not agree with the particular needs of the installation.

Also the installation of important elements of disparate companies tends to complicate the system, involving several people repairing possible breakdowns, making future modifications or even commissioning.

It is becoming more and more important to be able to act remotely on the control elements, both for the adjustment as for the diagnosis of faults or the simple supervision of the system. A dispersed control makes difficult these actions since only a small part of the information of the different elements are accessible to the control system.

A dispersed system may be enough for certain applications, but it is an important limitation as current management systems need the largest possible amount of data to optimize plant production to the maximum. Another factor in favor of the Bobitecnic SCDi system is that it is fully customizable and therefore able to adapt to the particular characteristics of each installation.

DETAIL OF THE SYSTEM COMPONENTS:

This system allows the control of the speed of the generator from the frequency of the remaining voltage of the generator. The system does not need any external mechanical or electrical equipment because it performs the measurement through the voltage reference of the generator itself. The high precision and speed of this reading allows the machine to be placed in synchronous conditions without the help of external elements.
Possibility of a redundant speed detection system by gearwheel and inductive sensors.

Control of speed with control of the regulating systems with proportional valves

The turbine speed regulating program consists of a closed loop with double feedback that drives a set of proportional valves located in the hydraulic control group.
The control systems with proportional valves make the movements of the regulating systems with an accuracy and smoothness impossible to achieve with direct valve control systems that always produce more or less abrupt variations of the generation conditions causing additionally extremely long synchronization periods.
The characteristics of the regulation are of acceleration tachometer origin with a nominal speed setpoint through a loop P I D, completely digital, feedback by the position of the regulating system and the acceleration of the machine. The acceleration control system makes it possible to perform synchronization maneuvers much faster regardless of the changes produced by the variation of net jump or any other variable involved in the regulation. The acceleration setpoint is variable as a function of the nominal speed and becomes zero when the machine is at the synchronizing speed. The control system performs automatic recalibrations of the speed control system and monitors its operation within the preset limits.
Once the generator is coupled to the grid the system calculates the position of the regulating systems depending on different variables such as: turbine type, load curve, net jump, time period, water reserve, turbine performance,  Opening limiter and others.
When the desired positions of the regulating systems have been established these are brought to them through a closed loop P I D regulation loop.
The interaction of different variables such as power and level or flow rate available and the control system of the regulating devices allows, in the machines of more than one regulating system (Kaplan or Pelton) the progressive increase without sudden jumps of the power and the optimization of efficiency according to the curves of each machine. This feature is very important in specific moments in which the available flow exceeds in few points the maximum performance.

Automatic synchronization:

Once the generation voltage reaches a minimum value and after verification of the voltage level in the network the synchronization system proceeds to equalize the generating voltage with the one of the external network, once this equality is achieved the system conducts the Machine to optimum synchronization conditions and an external synchronizing relay gives the order of connection of the coupling circuit breaker. The voltage equalization prior to the synchronization maneuver is a determining factor for the coupling speed.

Digital exciter control:

Another of the integrated systems is the one related to the electronic equipment of control of the exciter of the generator, the system of regulation is digital and allows ramps of excitation, the easy modification of the regulation setpoints, fixation of maximum and minimum levels of excitation as well as once coupled, the regulation by setpoint of reactive power.

As this is a digital procedure the values obtained are adjusted with great precision to the preset setpoints.

By having total control of the excitation the integrated system facilitates the installation of protections that are not usually installed in machines of small and medium power such as the control of impedance of the system of generation.

Temperature Protection and control:

The system includes the connection of temperature sensors of PT100 type intended for the protection of bearings, windings and cooling systems as well as their display and trigger setpoints.

Protection and control of Electrical generation parameters:

The integrated system collects the electrical data of the generation from a digital analyzer of the electrical parameters that provide the most recent values:

• Voltage, current, active power, reactive power, cosine, active energy meter and reactive energy meter
• All this information is treated for later collection from the telecontrol system and to stablish the alternative protection systems.
  

Remote control system via telephone network:

Remote control system via telephone network allows us to control the operation of the turbine from a compatible computer i5 or higher with 8 Gb of RAM through a modem and the CRT control program developed in windows environment.

This system allows to see all the turbine operating variables, such as: position of all control devices, water level, instantaneous power, energy production, bearing and winding temperatures, etc. from one or more remote positions. That is, all the information available within the PLC.

The PLC also has a historical record capable of storing the 8-day production curve, as well as the last 20 alarms that occurred, with the corresponding moment of appearance. This historical record, when we connect with the CRT telecontrol program, we store it to the PC and then in this PC, not having to be communicating with the PLC, we can see:

• The production curve of the generator in integrations of 15 minutes.
• Alarms occurring in relation to the graph or separately.
• The production reports of the plant.

The installation of the telecontrol system makes it possible to make corrections and adjustments to the control program of the PLC without having to go to the central office by our personnel, as well as the support for the location of possible faults in the control panel.

For more information on the telecontrol system there is a specific manual for this.

Tele-alarm system via telephone network

Telephone teller capable of giving the power plant alarms or blocking alarms by means of 2 oral messages to 4 telephones programmable through the CRT remote control program controlled by variables to be defined by those responsible for the operation.
 

Local data display system

Operator terminal consisting of a 122 x 67 mm 42 x 16 character backlit alphanumeric display which communicates via the DF1 protocol to the CPU of the control system.

There are three user definable screens dedicated to the presentation of variables and states of the installation, two screens dedicated to the display of alarms and shots, and two screens of instructions accessible to the operator through a key.
 

List of power plants with the Bobitecnic SCDi system: